This application is related to a co-pending U.S. patent application Ser. No. 13/993,196, filed on the same day as this application, the disclosure of which is incorporated herein in its entirety.
1. Field of the Disclosed Embodiments
This disclosure relates to systems and methods for employing information from platform sensors to trigger re-beamforming for a 60 GHz communication link.
2. Related Art
Before 2000, wireless telecommunication services were generally confined to the range of 2 to 30 GHz. An increasing demand for bandwidth, however, demonstrated the inadequacy of the traditional microwave frequency allocation. The wireless industry, more than a decade ago began to focus on the millimeter wave (MMW) frequency region of the electromagnetic spectrum between 30 GHz and 300 GHz to expand communication capacity. In 2001, the Federal Communications Commission (FCC) set aside a continuous block of 7 GHz of spectrum between 57 and 64 GHz for “unlicensed” wireless communications.
The 60 GHz MMW region of the spectrum became a focus of study based its unique characteristics. Wireless communications in the 60 GHz frequency range experience a high level of atmospheric radio frequency (RF) energy absorption. For many years, the intelligence community had operated wireless systems at 60 GHz because this high level of atmospheric absorption attenuates the transmitted signals over distance, allowing the signals to be very focused. Based on the years of use, the characteristics of this frequency range were well known and well documented. Understanding that the transmitted RE energy in this frequency region would be quickly absorbed by oxygen molecules in the atmosphere over long distances, wireless technology developers began to focus on this characteristic as a benefit for certain applications.
Previously, the high levels of atmospheric absorption and resultant range limitations were viewed as rendering MMW technologies unsuitable for certain wireless applications. As there emerged a need for short-range, focused and potentially secure transmission paths, however, MMW technologies, and particularly 60 GHz MMW systems, were viewed as presenting possible solutions worthy of further study. The unique characteristic of limited energy propagation in an oxygen atmosphere for transmissions in the 60 GHz band was found to present significant benefits such as increased immunity to interference for transmitter/receiver systems in comparatively close proximity to one another leading to a greater degree of potential frequency re-use in a local environment.
Transmitting in the 60 GHz wavelength range results in a fairly focused beam as compared to transmitting in lower frequency ranges. It is this pencil beam transmission capability combined with high energy absorption outside the narrow transmission beam that provides the unique ability to reuse a same frequency in a comparatively localized region making it possible to operate multiple transmitter and receiver combinations on the same frequency in close proximity to one another with very low likelihood of interference.
Another benefit of the use of MMW frequencies lies in the relationship between signal wavelength and antenna size. Transmitters and receivers operating in the MMW region use high-gain antennas to focus as much of the transmitted signal as possible onto the receiving antenna, thereby overcoming the effects of atmospheric absorption in the pencil beam between the transmitter and the receiver. Those of skill in the art recognize that, with an increase in RE frequency, wavelength decreases. This makes it possible to produce required gains with smaller antennas. Thus, at 60 GHz, a very compact, low-cost antenna can be used to achieve a highly focused beam. This architecture results in the emissions from the MMW system via a high-gain/narrow beam antenna being very narrow and focused. Directivity is a measure of how well an antenna focuses its energy in an intended direction. Point-to-point radios should have highly directional antennas in order that all the transmitted energy is directed just at the intended recipient. Highly focused antennas minimize the possibility of interference, minimize the risk that the transmission will be intercepted, and maximize performance. These all were found to be tremendous advantages in the employment of the 60 GHz frequency range for wireless communication.
Against the backdrop of the above advantages, 60 GHz MMW communication suffers from certain shortfalls based on the above-discussed characteristics as well. Among these shortfalls is that 60 GHz communication is, by its very nature, highly susceptible to human blockage. Further, because the 60 GHz transmission beam is so narrowly focused for directional transmission, it is very vulnerable to device movement and rotation. Either of these occurrences can result in significant link degradation. As a result, mechanisms to cope with link degradation due to blockage and/or device movement become of critical importance in sustaining robust 60 GHz communication links.
Among the conventional methods for dealing with link degradation in a 60 GHz link is to employ Modulation Code Scheming (MCS) adaptation using various radio technologies. While adaptation can cope with many issues regarding link degradation, it does not necessarily aid in maintaining optimal link performance in the event of occurrences such as device rotational or translational movement. In these instances, the directional beam of the 60 GHz link may fall completely off the communicating peer device's reception beam. A better strategy for dealing with these occurrences is to perform re-beamforming to find a stronger communication path.
Those of skill in the art recognize that the term “beamforming” refers to a class of well-known signal processing techniques used in certain antenna arrays for manipulating directional signal transmission or reception. One technique is to combine elements in the particular antenna array in a way that signals at particular angles experience constructive interference, while other signals experience destructive interference. Beamforming, therefore, takes advantage of interference to change the directionality of the array. Beamforming can be used at both the transmitting and receiving ends in order to achieve spatial selectivity.
Re-beamforming is a process that can be used to strengthen a weakening communication link, otherwise to re-establish a broken communication link.